A287834 Number of words of length n over the alphabet {0,1,...,10} such that no two consecutive terms have distance 3.
1, 11, 105, 1005, 9621, 92105, 881753, 8441329, 80811789, 773639469, 7406320733, 70903294113, 678781988705, 6498216958121, 62209699634757, 595555173609653, 5701457600593525, 54582044135967257, 522532964509030377, 5002390498942001761, 47889630709552579709
Offset: 0
Links
- Index entries for linear recurrences with constant coefficients, signature (10,-2,-21,10).
Crossrefs
Programs
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Mathematica
LinearRecurrence[{10, -2, -21, 10}, {1, 11, 105, 1005, 9621}, 20]
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Python
def a(n): if n in [0,1,2,3,4]: return [1, 11, 105, 1005, 9621][n] return 10*a(n-1) - 2*a(n-2) - 21*a(n-3) + 10*a(n-4)
Formula
a(n) = 10*a(n-1) - 2*a(n-2) - 21*a(n-3) + 10*a(n-4), a(0)=1, a(1)=11, a(2)=105, a(3)=1005, a(4)=9621.
G.f.: (-1 - x + 3*x^2 + 2*x^3 - 2*x^4)/(-1 + 10*x - 2*x^2 - 21*x^3 + 10*x^4).
Comments